1. Field of the Invention
This invention relates generally to electrical connectors for use with printed circuit board assemblies. More particularly it relates to connectors of the type incorporating a mechanism for retracting circuit contacts, thereby yielding a low or zero insertion force required for inserting an associated printed circuit board assembly. Still more particularly, the invention relates to an improved electrical connector having an improved linear cam contact actuating mechanism.
2. State of the Prior Art
Printed circuit board assemblies for mounting and interconnecting electronic components are well-known. Various types of connectors for making physical and electrical interconnection with printed circuit board assemblies are also well-known. Multiple printed circuit board assemblies are often interconnected through associated connectors in panel-type assemblies.
As technology provides for the fabrication of integrated circuits having ever-increasing numbers of circuits per integrated circuit chip, it becomes desirable to provide increased number of connector contacts on the mounting multilayer printed circuit boards so that interconnections can be made through the system. The smaller sizes of integrated circuit packages with their increasing number of pin contacts, has resulted in multilayer printed circuit assemblies that have insufficient pin connections along a single edge to make the requisite contact connections in the system. This has led to the development of providing connector contacts along the side edges of the multilayer printed circuit assembly, as well as at the back or internal edge of the assembly. Such arrangement of course must account for the insertion and removal of printed circuit board assemblies.
A connector arrangement permitting making contact on three sides of a multilayer printed circuit board assembly can include a connector mounted on the rear edge of the printed circuit board assembly that mates with a connector block assembly mounted in the back panel of the cabinet housing. Connectors of this type utilize mating pin and receptacle combinations that provide electrical connection and are retained in place by the friction contact between the pins and mating receptacles when the assembly is inserted. In order to facilitate insertion and removal of the printed circuit board assembly, it is desirable to have the connectors associated with the side edges of the assembly to be of a type that can be activated into making electrical contact after the assembly is inserted in the back panel connectors, and to disengage electrical and physical contact prior to attempting to remove the assembly from the cabinet.
Connectors exist in the prior art having connector electrical contacts for engaging electrical contact surfaces on associated printed circuit board assemblies, and including actuating mechanisms for urging the connector contacts out of engagement with the printed circuit board assembly. With the connector contacts retracted, the associated printed circuit board assembly can be inserted in the connector utilizing very little insertion force. This low insertion force gives rise to the name Zero Insertion Force (ZIF) connectors. Advantages of ease of insertion and removal of the printed circuit board assembly, minimization of contact wear, and maximization of the number of connector contact for this type of connector have been recognized and described in the prior art.
One example of a low insertion force cam actuated printed circuit board connector is disclosed in U.S. Pat. No. 3,899,234 to Yager et al. It describes an arrangement having a plurality of electrical contacts to be brought into contact with an associated printed circuit board through cam actuation. It describes an elongated contact drive member lying freely at the bottom of a printed circuit board receiving aperture, and is utilized to cause movement to a drive member for opening and closing the contacts. It relies mainly on the spring action of the contact for causing the contacts to close.
Another type of low insertion force cam actuated printed circuit board connector is shown in U.S. Pat. No. 3,478,301 to Conrad, et al. It describes a connector having a plurality of contacts held normally open for allowing ease of insertion of a printed circuit board. Before the printed circuit board is completely inserted, it engages a rotatable cam mechanism that causes the contacts to be brought into contact with the printed circuit board as the board is completely inserted. This type of cam operation of course requires that the printed circuit board be inserted parallel to the contact.
A connector having a hollow shell mounted over contacts and vertically movable within a housing, with the shell activated by an elongated cam rod inside the outer housing, is described in U.S. Pat. No. 4,021,091 to Anhalt et al. The cam is shown to be longitudinally movable to shift the shell downwardly for cam actuating the contacts.
A connector that functions to make contact with a printed circuit board within a matched pair of camming blocks is described in U.S. Pat. No. 3,997,231 to Sherwood. The contact activation is caused by moving a sliding exterior member. The exterior cam activator includes pairs of inclined slots, one pair positioned at each end of the connector, and arranged to cooperate with a pair of rods spanning the internal width of the connector. The rods in the associated slots are arranged such that the axes of the rods describe a horizontal plane and determine the relative position of the connector elements.
Another type of low insertion force connector for making electrical connection between a printed circuit board and other circuitry is described in U.S. Pat. No. 4,179,177 to Lapraik. A connector having an elongated outer housing with a longitudinal channel along the bottom thereof and having ramps formed in the bottom of the channel is described for cooperating with a plurality of contacts mounted within the outer housing on either side of the channel. An elongated cam is arranged for operation within the channel and cooperates with an inner housing for causing the contacts to be open and closed as the cam is moved upwardly and downwardly on the ramp. The cam is shown to have an inclined slot at each end thereof. Pins are inserted through the outer housing and the associated slots for causing an upwardly and downwardly extending force as the cam is moved backward and forward. The slots through the cam are positioned such that the strength of the cam member is greatly reduced and is a source of failure of the connector.
The connectors that require transverse pins or rods for cooperation with the camming mechanism preclude the connectors from being mounted closely together if repair of the connector is to be accomplished without totally disconnecting the connector from its associated support assembly.